Glossary of terms


A protein produced by the body’s immune system when it detects harmful substances called antigens.


A molecule capable of triggering an immune response.


A sensation sometimes experienced before a seizure ‘properly’ begins. It can be anything from a sound, smell, feeling, taste, change in body temperature or disturbance in vision. Auras can occur minutes/hours before the seizure, giving the person enough warning to take necessary action to prevent injury.

Auras are themselves simple focal seizures and their nature depends on where in the brain they originate. In some cases the epileptic activity spreads to include the majority of the brain, resulting in a generalised seizure such as a tonic-clonic seizure. This is known as ‘secondary generalisation’.

Autoimmune disease

This is a condition in which the body produces an abnormal immune response to some of its own cells/tissues.


This is a biological molecule found in the blood, other body fluids, or tissues that is a sign of a normal or abnormal processes, or of a disorder. Biomarkers are sometimes used to see how well the body responds to a medical treatment. Sometimes processes/outcomes are difficult to measure, but there may be a biomarker that is strongly correlated with a process/outcome that is easier to measure and can be used instead.


One of more than a 100 active cannabinoids identified in cannabis. Research has shown that cannabidiol may be beneficial in reducing seizure frequency in epilepsy. Clinical trials are ongoing.

Childhood epilepsy syndromes

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Clinical trials

These are used to investigate, in humans, the safety and effectiveness (compared to a placebo or standard treatment) of prospective new drugs and devices (‘interventions’). Interventions must successfully compete a number of clinical trial ‘phases’ before being considered for licensing and subsequent marketing. More details can be outlined here.


The presence of one or more additional conditions occurring alongside a primary condition. Common comorbidities of epilepsy include depression, anxiety and autism.


The folded outer surface of the brain.

Cortical dysplasia

A congenital abnormality whereby the neuron networks in a particular area of the brain fail to form properly during development and some neurons grow to be larger than normal in certain regions. This causes the signals sent through these neurons to misfire, which can lead to seizures.


DNA is short for deoxyribonucleic acid. It is the molecule found in most of our cells that contains the genetic code, or blue print, that makes us who we are. It tells our body what proteins to make, but it also contains sections that do not make proteins. Also see RNA.

Focal seizures

Seizures that affect a particular part/parts of the brain. Consciousness may be altered but is not always lost.

See our online leaflet for more information.


See ‘Neurotransmitter

Gap junction

A specialized connection between certain types of cell, which allows charged particles (ions) such as calcium (Ca2+), chloride (Cl-), sodium (Na+) and potassium (K+) to pass freely between cells.

Gene expression

The process whereby the information held in a gene is used to create a functioning gene product, very often a protein. If a gene is under-expressed, less of the gene product will be produced than normal, whereas if the gene is over-expressed, more of the product will be formed than normal.

Generalised seizures

Seizures that involve large areas on both sides of the brain and often cause a loss of consciousness.

See our online leaflet for more information.

Glial cells

Cells that surround neurons and provide them with support, oxygen, nutrients, insulation and protection from germs.


See ‘Neurotransmitter

Grey matter

The darker tissue of the brain and spinal cord, made up mainly of nerve cell bodies and branching dendrites (see neurons).


A gap junction is made of two hemichannels, which connect to each other across the space between the two cells.

Hippocampus (plural: hippocampi)

This is an important memory centre in the brain, located deep within the temporal lobes.

Immune system

The mechanisms that protect the body against disease and unwanted ‘foreign’ bodies.

Ion channels

Pores that help to control electrical activity in cells, by allowing the flow of ions such as calcium (Ca2+), sodium (Na+) and potassium (K+) into or out of the cell. A channel that allows the passage of potassium is known as a potassium channel and so forth.

Ketogenic diet

A high fat, low carbohydrate, ‘normal’ protein diet that is sometimes used as an add-on treatment in people with drug-resistant epilepsy. Most evidence for its success currently comes from trials in children.


Excitable cells that are a core component of the brain and spinal cord. Neurons receive, process and transmit information, and they play a vital role in all of our functions. Information travels down neurons as electrical signals, which are created by the movement of ions into and out of the cell membrane, via ion channels. The image below shows the structure of a neuron (ref:

Diagram of a neuron


A chemical that carries messages between neurons and other cells, across synapses. A neurotransmitter can be excitatory, meaning that it triggers the next cell to become active; or inhibitory, meaning that the next cell is silenced.

The major excitatory neurotransmitter in the brain is called glutamate, whilst the main inhibitory neurotransmitter is known as GABA.


An inactive substance designed to look like the drug being tested in a clinical trial and used to rule out any psychological effects that the simple act of taking a ‘treatment’ might have on the recipients.


A structure or site, found on the surface of a cell, or within a cell, that can bind to a particular hormone or neurotransmitter. The binding of a substance to its receptor begins a chain of biochemical reactions that lead to changes in the cell. For example it might cause an influx of a particular ion, or a change in enzyme activity.

Refractory epilepsy

Also known as drug-resistant or intractable epilepsy: “The failure of adequate trials of two tolerated and appropriately chosen and used anti-epileptic drugs (whether as monotherapies or in combination) to achieve sustained seizure freedom.”


RNA is short for ribonucleic acid and is a molecule that comes in several types. Genetic information from DNA is transferred to RNA, which tells the cell which amino acids (building blocks of proteins) to include when assembling a protein.

Seizure types

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Status epilepticus (SE)

SE is a condition in which seizures fail to terminate in the usual way, leading to either a prolonged seizure, or consecutive seizures without recovery of consciousness in between. For tonic-clonic seizures, evidence suggests that treatment for SE should begin once a seizure, or series of seizures, has lasted five or more minutes. Treatment usually starts with a benzodiazepine drug, e.g. diazepam, midazolam or lorazepam, and an intravenous anti-epileptic drug is often added if the SE hasn’t resolved 30 minutes after the start of therapy.

In cases where SE hasn’t responded treatment after an hour and a half (‘refractory SE‘), additional anaesthetic therapy may be needed. The term ‘super-refractory SE’ refers to SE that continues or recurs 24 hours or more after the start of the treatment.

After a certain length of time (reportedly 30 minutes for tonic-clonic seizures), SE can have long-term consequences, including neuronal death, neuronal injury, and alteration of neuronal networks.


A small gap between a neuron and another cell type, across which signals are carried in a chemical form, by neurotransmitters. The region at the end of a neuron where neurotransmitters are released is known as the pre-synaptic membrane. Once a neurotransmitter has crossed a synapse, it binds to a specific receptor on the membrane of a connecting neuron. This is called the post-synaptic membrane.

If the neurotransmitter released into a synapse is excitatory, the synapse is called an excitatory synapse. If the neurotransmitter released is inhibitory, the synapse is known as an inhibitory synapse.


A structure of two halves that lies deep within the brain and plays a vital role in the relaying of sensory and motor signals, and the regulation of consciousness and sleep.

Tuberous sclerosis (also known as tuberous sclerosis complex)

A rare genetic condition that causes mainly non-cancerous growths to develop in different parts of the body, most often the brain, heart, skin, kidneys, eyes and lungs. People in whom the brain is involved commonly develop epilepsy.